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Questions and Answers
What structure is formed from the ectoderm during eye development?
What structure is formed from the ectoderm during eye development?
At which week does the invagination of the optic vesicle become pronounced to form the choroid fissure?
At which week does the invagination of the optic vesicle become pronounced to form the choroid fissure?
What is the consequence of the failure of the choroid fissure to close?
What is the consequence of the failure of the choroid fissure to close?
Which structure is responsible for forming the pigmented epithelium of the retina?
Which structure is responsible for forming the pigmented epithelium of the retina?
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What happens to the hyaloid vessels during eye development?
What happens to the hyaloid vessels during eye development?
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At what stage do the eyelids open during development?
At what stage do the eyelids open during development?
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Which layer of mesenchyme vacuolizes to form the anterior chamber of the eye?
Which layer of mesenchyme vacuolizes to form the anterior chamber of the eye?
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What structure partially derives from the epithelial layer of the optic cup?
What structure partially derives from the epithelial layer of the optic cup?
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What is the primary purpose of the iris in the eye?
What is the primary purpose of the iris in the eye?
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Which of the following best describes the role of the retina?
Which of the following best describes the role of the retina?
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What condition is associated with opacity in the lens of the eye?
What condition is associated with opacity in the lens of the eye?
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How do rods and cones differ in their functional characteristics?
How do rods and cones differ in their functional characteristics?
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In what area of the retina is visual acuity highest?
In what area of the retina is visual acuity highest?
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What is the main structural characteristic of the cornea?
What is the main structural characteristic of the cornea?
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What occurs at the optic disc?
What occurs at the optic disc?
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What type of humor fills the anterior and posterior compartments of the eye?
What type of humor fills the anterior and posterior compartments of the eye?
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Which statement accurately describes the uvea?
Which statement accurately describes the uvea?
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What is the primary reason for the increased sensitivity of rods compared to cones?
What is the primary reason for the increased sensitivity of rods compared to cones?
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What forms the vascular and fibrous coat of the eye during development?
What forms the vascular and fibrous coat of the eye during development?
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What structure gives rise to the iris during eye development?
What structure gives rise to the iris during eye development?
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What is the primary effect of a coloboma in the eye?
What is the primary effect of a coloboma in the eye?
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What is the primary structural component of the sclera?
What is the primary structural component of the sclera?
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Which layer of the optic cup is responsible for the photoreceptive retina?
Which layer of the optic cup is responsible for the photoreceptive retina?
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Which cells in the retina are responsible for color vision?
Which cells in the retina are responsible for color vision?
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How do the rods contribute to vision in low light conditions?
How do the rods contribute to vision in low light conditions?
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At what point does the optic nerve myelination become complete during postnatal development?
At what point does the optic nerve myelination become complete during postnatal development?
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Which structure is responsible for the accommodation of the lens?
Which structure is responsible for the accommodation of the lens?
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Which structure forms the opening that will become the pupil during eye development?
Which structure forms the opening that will become the pupil during eye development?
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What is the significance of the fovea centralis in the retina?
What is the significance of the fovea centralis in the retina?
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What happens to the hyaloid vessels during eye development?
What happens to the hyaloid vessels during eye development?
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What consequence does the failure of the iridopupillary membrane to obliterate have?
What consequence does the failure of the iridopupillary membrane to obliterate have?
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Which layer of the eye is involved in supplying nutrients to the retina?
Which layer of the eye is involved in supplying nutrients to the retina?
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What happens at the optic disc?
What happens at the optic disc?
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What characteristic is associated with congenital cataracts during intrauterine life?
What characteristic is associated with congenital cataracts during intrauterine life?
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Which feature develops from mesenchyme adjacent to the optic cup?
Which feature develops from mesenchyme adjacent to the optic cup?
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What role does the iris play in vision?
What role does the iris play in vision?
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Which statement best describes the retina's structure?
Which statement best describes the retina's structure?
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What is the primary composition of the anterior chamber of the eye?
What is the primary composition of the anterior chamber of the eye?
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Study Notes
Eye Development Timeline
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Day 22:
- Neuroectoderm forms the retina, iris, and optic nerve.
- Ectoderm forms the lens.
- Mesoderm forms the vascular and fibrous coat of the eye.
Eye Development: Weeks 5-7
- Week 5: Optic vesicle forms.
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Week 7:
- The optic vesicle invaginates forming the optic cup.
- The choroid fissure forms, a cleft in the optic cup.
- The future pupil forms as a round opening in the optic cup.
Further Development
- Optic Cup: Forms the pigmented epithelium (outer layer) and photoreceptive retina (posterior 4/5 of the eye).
- Ciliary Body: Partially derived from the epithelial layer of the optic cup and adjacent mesenchyme.
- Iris: Posteriorly covered by the epithelial layer of the optic cup, giving rise to the sphincter pupillae and dilator pupillae. The anterior iris is derived from mesenchyme.
- Optic Stalk: Forms the optic nerve. The anterior portion of the hyaloid vessels become a remnant (hyaloid canal of the vitreous body). Myelination of the optic nerve is complete by 10 weeks postnatally.
- Meninges: Surround the optic stalk. Dura matter connects to the sclera.
- Sclera: Forms from mesenchyme adjacent to the optic cup.
- Anterior Chamber: Mesenchyme anterior to the lens vacuolizes, forming the anterior chamber of the eye.
- Cornea: Mesenchyme is split into an inner layer (iridopupillary membrane) and an outer layer (cornea).
- Eye Chambers: The iridopupillary membrane obliterates, opening communication between the anterior and posterior chamber.
- Eyelids: Open around week 26.
Congenital Defects
- Coloboma Iris: Occurs when the choroid fissure fails to close completely. This can affect the iris, ciliary body, retina, and optic nerve.
- Congenital Cataracts: The lens becomes opaque during fetal development, often due to gene mutations.
Remnants
- Remnants of the Iridopupillary Membrane: Remain in the iris at the pupillary aperture.
Eye Histology
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Cornea:
- Transparent and densely innervated.
- Avascular.
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Sclera:
- Posterior 5/6 of the eye.
- Rich in collagen and elastic fibers.
- Avascular.
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Lens:
- Avascular.
- Elasticity decreases with age.
- Opacity in the lens (cataract).
-
Uvea:
- Consists of the choroid, iris, and ciliary body.
- The ciliary body contains the suspensory ligaments that support the lens and the ciliary muscle for accommodation.
-
Retina:
- Outgrowth of the diencephalon.
Iris & Pupil
- Iris: Controls the amount and quality of light entering the eye.
- Pupillary Sphincter: Constricts the pupil (miosis).
- Pupillary Dilator: Dilates the pupil (mydriasis).
- Autonomic Nervous System (ANS): Modulates iris function.
Eye Chambers
- Anterior Chamber: Filled with aqueous humor.
- Posterior Chamber: Filled with aqueous humor.
- Posterior Compartment: Filled with gelatinous vitreous humor.
Retina
-
Seven Retinal Cell Types:
- Outer facing the choroid layer.
- Inner layer facing the vitreous humor.
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Photoreceptors: Rods and cones.
- Rods: 125 million/retina. 20:1 ratio of rods to cones.
- Cones: 3 types (RBG).
- Rods: Contribute to night vision (scotopic).
- Cones: Contribute to daytime vision (photopic).
-
Convergence:
- Rods: 10-100 rods converge onto 1 bipolar cell
- Cones: 1 cone to 1 bipolar cell = more acuity
Fovea & Macula Lutea
-
Fovea Centralis:
- Sharpest vision.
- Acute color discrimination.
-
Macula Lutea:
- Area of central vision.
Retina Specialization
- Blind Spot: Does not have photoreceptors.
- Peripheral Retina: Higher density of rods and cones compared to the fovea.
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Fovea: Rich in cones.
- Specialized in high-light vision.
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Peripheral Retina:
- Specializedin low-light vision.
Optic Nerve
- Optic Nerve: Exits the eyeglobe and is surrounded by all three meninges (dura mater, arachnoid mater, pia mater).
Eye Development Timeline
- Day 22: Neuroectoderm forms the retina, iris, and optic nerve.
- Week 5: The optic vesicle begins to invaginate.
- Week 7: The optic vesicle invagination expands inferiorly, creating a cleft called the choroid fissure.
- Later: The mouth of the optic cup forms a round opening, which becomes the future pupil.
Eye Development Processes
- Optic Cup: Forms the pigmented epithelium (outer layer) and photoreceptive retina (posterior 4/5 of the eye).
- Ciliary Body: Develops partially from the optic cup's epithelial layer and partially from adjacent mesenchyme.
- Iris: Covered posteriorly by the optic cup's epithelial layer (forming the sphincter pupillae and dilator pupillae) and anteriorly derived from mesenchyme.
- Optic Stalk: Develops into the optic nerve.
- Hyaloid Vessels: Obliterate and become a remnant (hyaloid canal of the vitreous body).
- Optic Nerve Myelination: Completes around 10 weeks after birth.
- Optic Stalk Meninges: Surrounded by the brain's meninges, with the dura mater continuing into the sclera.
- Sclera Formation: Mesenchyme adjacent to the optic cup forms the sclera.
- Anterior Chamber Formation: Mesenchyme anterior to the lens vacuolizes, creating the anterior chamber of the eye.
- Iridopupillary Membrane: Mesenchyme is split by the chamber into an inner layer (iridopupillary membrane) and outer layer (cornea).
- Anterior and Posterior Chamber Communication: The iridopupillary membrane obliterates, opening communication between the anterior and posterior chambers of the eye.
- Eyelid Opening: Occurs around week 26.
Eye Development Defects
- Coloboma Iris: The choroid fissure fails to close, leaving a cleft. This can affect iris, ciliary body, retina, and optic nerve.
Remnants of Iridopupillary Membrane
- Iris: The iris is formed from the remaining iridopupillary membrane, which forms the pupillary aperture.
Congenital Cataracts
- Lens Opacity: The lens becomes opaque during fetal development, often due to gene mutations.
Eye Histology:
- Cornea: Transparent, densely innervated, and avascular, forming the front of the eye.
- Sclera: Posterior 5/6 of the eye, rich in collagen and elastic fibers, also avascular.
- Lens: Avascular, progressively less elastic with age, opacity leads to cataracts.
-
Uvea: Includes the choroid, iris, and ciliary body.
- Choroid: Provides blood supply to the retina.
- Iris: Controls light entering the eye.
- Ciliary Body: Contains suspensory ligaments and ciliary muscle for lens accommodation.
- Retina: An outgrowth of the diencephalon, responsible for photoreception.
Eye Function:
- Pupillary Sphincter (miosis): Constricts the pupil, reducing light entering the eye.
- Pupillary Dilator (mydriasis): Dilates the pupil, increasing light entry.
- Autonomic Nervous System (ANS): Modulates pupil size.
Eye Chambers:
- Anterior Chamber: Located between the cornea and iris, filled with watery aqueous humor.
- Posterior Chamber: Located between the iris and lens, also filled with aqueous humor.
- Posterior Compartment: Located behind the lens, filled with gelatinous vitreous humor.
Retina Structure:
- Seven Retinal Cell Types: Consist of rods, cones, bipolar cells, ganglion cells, amacrine cells, horizontal cells, and Müller cells.
- Retinal Layers: Organized into distinct layers, with the outer layer facing the choroid and the inner layer facing the vitreous humor.
Photoreceptors:
- Rods and Cones: Contain light-absorbing photopigments.
- Rods: Contribute to night vision (scotopic).
- Cones: Function in daytime vision (photopic) and detect different colors.
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Convergence: Rods converge onto bipolar cells, while cones have a 1:1 ratio with bipolar cells.
- Rods: High convergence, leading to lower visual acuity.
- Cones: Low convergence, leading to higher visual acuity.
Retina Regions:
- Optic Disc or Papilla: The blind spot where the optic nerve exits the eye.
- Fovea Centralis: The area of sharpest vision and acute color discrimination.
- Macula Lutea: The area of central vision, containing the fovea.
- Retinal Specialization: The retina is regionally specialized, with no photoreceptors in the blind spot and a higher density of rods and cones in the periphery. The fovea is rich in cones, specialized for high light vision, while the periphery is more suited for low light vision.
Optic Nerve:
- Meningeal Layers: The optic nerve is invested by all three meningeal layers as it exits the eye.
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Description
Explore the intricate process of eye development from day 22 through vital weeks 5 to 7. This quiz covers the formation of essential structures such as the retina, iris, optic nerve, and more. Test your knowledge of embryological milestones in eye formation.
